(HealthDay News) -- As the debate continues about the best time for mammograms, the American College of Obstetricians and Gynecologists (ACOG) is asking women to add their voice to the discussion.

In updated guidelines on breast cancer screening for average-risk women, ACOG emphasized shared decision-making between a woman and her doctor about when to start mammography screening and how often to do it.

"What is critically important is that the patient's value and preferences are factored into that decision-making process," said Dr. Christopher Zahn, ACOG's vice president of practice activities.

The new guidelines, Zahn said, are "empowering women to be involved in that decision."

ACOG recommends that women at average risk of breast cancer be offered screening mammography beginning at age 40. The decision about whether to start at that age, however, should be made by a woman and her doctor. The discussion should include information about benefits and harms.

If a woman doesn't start screening in her 40s, she should begin no later than age 50, the guidelines state.

Repeat screening every one or two years is recommended, based on more discussion, the guidelines suggest. Those at average risk should continue screening until at least age 75. After 75, the decision, again, should be based on a discussion with the doctor and include information about the woman's health status and expected longevity.

The new guidelines evolved after experts reviewed recent research on mammography, Zahn said.

A discussion between a woman and her doctor should include information on both benefits and harms, Zahn said. For younger women, he said, the ratio of benefits to harms is a little lower, he said, because the incidence of breast cancer in younger women is generally lower.

Among the potential harms are callbacks for more testing and biopsies for lesions that turn out to be benign, Zahn said. A woman who is concerned about the potential harms may decide to delay screening until later, he said.

Under the new guidelines, he said, "we acknowledge there are several approaches" and that women should choose a strategy that works best for them.

The other major organizations issuing guidance also stress that a woman discuss the pros and cons with her doctor when deciding on mammography.

Currently, the American Cancer Society guidelines say a woman at average risk can start mammograms at 40 if she chooses, but the group recommends that yearly mammograms begin at age 45. By age 55, a woman can choose to have the screening annually or every other year and can continue to discuss with her doctor the best screening regimen for her.

The U.S. Preventive Services Task Force guidelines recommend starting at age 50 for average-risk women and repeating the screening every two years. However, those guidelines also say women under age 50 should weigh the pros and cons and decide if they should begin screening earlier.

"The guidelines [from various groups] are all coming into line and becoming agreeable for a number of reasons," said Dr. Otis Brawley, chief medical and scientific officer at the American Cancer Society. One is recognizing the value of evidence-based medicine. Another, he said, is that "we are trying to respect people's rights to self-determination and making decisions for themselves.

"We are starting to realize it is likely that a few women in their 40s do benefit from mammography," Brawley said, but it is also likely that others are inconvenienced or harmed by the screening.

"Every medical intervention we do is always a balance between the benefits and the risks," he said.

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